In various fields of medicine and engineering it is often necessary to inspect surfaces that are difficult to reach. For example engine cylinders, compressors for jet aircraft engines, heat exchangers, internal organs, cavities, and arterial passageways in a patient. Biomedical imaging technology, for example, magnetic resonance imaging, X-ray computed tomography, ultrasound, and confocal microscopy can be used to inspect and characterize a variety of tissues and organs. However, there are many situations where existing biomedical diagnostics are not adequate. This is particularly true where high resolution, about 1 micron, imaging is required. Resolution at this level often requires biopsy and histopathologic examination. While such examinations are among the most powerful medical diagnostic techniques, they are invasive and can be time consuming and costly. Furthermore, in many situations conventional excisional biopsy is not possible. Coronary artery disease, a leading cause of morbidity and mortality, is one important example of a disease where conventional diagnostic excisional biopsy can not be performed. There are many other examples where biopsy can not be performed or conventional imaging techniques lack the sensitivity and resolution for definitive diagnosis.
A borescope is an optical device such as a prism or optical fiber that can be used to inspect inaccessible spaces. An endoscope is an instrument for visualizing the interior of a hollow organ like a colon or esophagus. The observed part of the internal surface can be illuminated with the help of the illumination channel and the optical observation system allows investigation of the internal space surface. During inspection it may be advantageous and important to investigate lateral surface in the space.
Elements allowing a change in the direction of optical observation permit inspection inside spaces and lateral surfaces that a rigid borescope or endoscope cannot view. Endoscopes and borescopes can include a means of articulating the tip of the scope so that it bends in several directions to look around a cavity. However, in many applications, for example arteries, there is insufficient room in the cavity or conduit for articulation of the scope tip.
Rather than being flexible, a rigid endoscope can contain a mount, an optical system for observation, and a light guide. The mount and the light guide can be placed in a tube housing. The optical axes of the observation and illumination system for lateral direction are deflected at an angle with respect to the lens optical axis with the help of a prism. In order to observe the entire lateral surface along the whole transverse perimeter of the investigated cavity, it is necessary to rotate the entire endoscope housing around the axis of symmetry. Fiber optic inspection devices may contains a lens in a mount and illumination lamps installed in a housing in a lateral wall of the housing in which a window is provided. Lateral observation can be performed due to a reflection prism situated opposite the window. For panoramic observation of the walls in a space the entire housing needs to be rotated. In some instruments the illumination source must also be rotated complicating the design and operation of such a device.
Current methods for screening and diagnosis of pathologic conditions in tissue such as cancer often involve surgical biopsy of the tissue followed by histological evaluation. This procedure is not only invasive, time-consuming and expensive but often is not capable of rapid and reliable screening of a large surface such as the colon, esophagus, or stomach. Since early diagnosis and treatment tend to be critical to effective and successful treatment of these pathologies, the development of better techniques and devices for diagnosis and screening would result in improved clinical outcomes.
Optical coherence tomography (OCT) is an imaging technique which allows high resolution observation and characterization of tissue microstructure imaging with resolution on the order of microns. This technique measures detailed changes within a few millimeters of a non-transparent tissue structure. One drawback of the OCT imaging is the time required to obtain images over a sufficient area.
Optical coherence domain reflectometry (“OCDR”) is an optical technique that uses a scanning Michelson interferometer in conjunction with a broadband illuminating source and cross-correlation detection. The similar technique of optical coherence tomography (“OCT”) can be used for imaging with catheters.
Both OCDR and OCT use optical data collected by a single mode optical fiber to determine the morphology, physical properties and location of various types of interspersed materials or biological tissue. Typically a probe used in conjunction with either OCDR and OCT includes an optical fiber having a head at its distal tip. Alternatively, the probe is formed by inserting an optical fiber concentrically into a thin-wall flexible hypodermic stainless-steel tube and fastening it with cement. A window in the tube allows light to pass to and from the head at the tip of the optical fiber. The probe is then inserted into the tissue or organ to be examined. Light emitted by the head of the optical fiber is reflected from the adjacent body of tissue or organ. The head then collects the reflected light, also known as “back-scattered” light.
Using a Michelson interferometer in conjunction with this apparatus the morphology, properties and location of the various materials, tissue or organ elements that caused the back-scattered light are determined and an image generated to provide a real-time visual display of the device, body of tissue, or organ being examined.
However, as a typical optical fiber can only emit light and gather back-scattered light along its axial centerline, it is limited to viewing straight ahead. A view transverse to the axial centerline of the fiber can be obtained by turning or bending the head of the fiber perpendicular to its axial centerline, and this is often very difficult or even impossible in the close confines typically encountered during surgical procedures, or in examining the sides of an artery or vein.
Mounting a gradient refractive index lens or a mirrored corner cube on the head of the optical fiber can be used to obtain lateral scans. Both a gradient refractive index lens or a mirrored corner cube deflect the emitted light at an angle transverse to the axial centerline of the optical fiber, and thus provide for lateral viewing. However, these apparatus add bulk to the head of the optical fiber. For example, the diameter of an optical fiber typically used in conjunction with OCDR and OCT is on the order of about 90 microns, while the diameter of the smallest GRIN lens is about 150 microns and that of the smallest mirrored corner cube is about 125 microns. The use of either of the aforementioned optical devices thus renders some locations inaccessible and makes the optical fiber more difficult to maneuver. In addition, extremely small GRIN lenses and mirrored corner cubes are quite expensive, and very fragile. Their use thus adds to the cost of the probe, and renders it prone to malfunction.
Embodiments of the present invention are devices that include two or more sample arms and one or more variable delay reference arms, the distal ends of the sample arms collecting source light backscattered from a sample. The backscattered light collected by the distal end of each sample or sensing arm is combined with reference light and low coherence interferometric signals for each sample arm produced in a single sweep of a variable delay of the device. The interference signal produced by the interaction of reference light and backscattered light for each sample arm is measured by a detector. Optionally the one or more sample arms have an adjustable delay. The devices of the present invention may be used to characterize a material using of low coherence light backscattered from the sample. These devices eliminate the need for optical switches or rotatable structures to sequentially address independent sample arms and permit the collection of low coherence source light backscattered from several different samples or from several different locations on a single sample utilizing a single sweep of one or more adjustable delays. The interference signals from device provides information on multiple surfaces of a sample and can be used to discriminate between healthy and diseased tissue without the need for rotating the probe or translating mirrors within the probe.
In one version of the device, two or more sensing or sample arms of an interferometer are coupled to one or more reference arms. The device can be used to obtain the low coherence interferometric (LCI) signals from all of the sample arms in a single long trace or sweep of one or more reference arms; each reference arm has a variable or adjustable delay. Optionally the sample arms may include an adjustable delay. The intensity of interference between the backscattered light from the sample and light from the reference section can be measured by a detector coupled to the reference arms and sample arms.
Another version the device is a sensor that includes two or more sensing arms, and a reference section with two or more arms where each reference arm has an adjustable delay. The sensing arms and the reference arm section are capable of being coupled to one or more low coherence light sources. The reference section and sample arms are configured to resolve interference of backscattered light and reference light from the two or more sensing arms in a single trace or sweep of the variable delay of the reference section. Optionally each sensing arms has an adjustable delay. The sample and reference arms can be configured in a relationship that permits acquisition of backscattering information from a sample and that can be used to improve signal averaging and noise reduction.
In another version of the device, two or more combined reference and sensing arms or probes of an autocorrelator are coupled with a delay compensator having a variable delay. LCI signals from interference between backscatter light collected by the probes and reference light from the probes can be separated or resolved during a single sweep of the delay compensator. The probe and delay compensator can be configured in a relationship that permits acquisition of backscattering information from a sample and that can be used to improve signal averaging and noise reduction. Optionally, each probe arm has an adjustable delay. The intensity of interference between the backscattered light and reference light can be measured by a detector coupled to the delay compensator section.
The devices of the present invention may include one or more low coherence light sources or they can be coupled to one or more exchangeable or pre-existing low coherence light sources. Optionally, the devices may be used for monitoring and delivering photodynamic therapy to a tissue. An activating light source may be coupled into the sample or probe arms of the devices for photodynamic therapy of a tissue. The sensor device may include a detector or it can be connected to an existing detector to measure the intensity of interference between the reference section light and backscattered light. The detector can include or may be connected to a processor that provides an output proportional to the interference between the backscattered light and reference arm light for each sensing or sample arm.
The sensors and apparatus in various versions of the invention can be included in a variety of inspection devices including but not limited to a borescope, endoscope, or catheter probe where the interference signals from the sensor provide simultaneously, information on the surface of the of the sample, and more preferable the sensor can discriminate between healthy and diseased tissue For example, an apparatus can include a guidewire, two or more light propagating probes in proximity, such as surrounding or being enclosed by, the guidewire. The probes propagate low coherence source light from a coupler or circulator into the sample and propagate backscattered light from the sample back to the coupler or circulator. The probes are coupled to interferometer or delay compensator that permits resolution of low coherence interferometric signals from one or more of the probes in a single scan of the adjustable delay in the compensator. An optical head that can direct source light to the sample in a variety of directions can be positioned on the distal end of the device; the optical head also collects backscattered light from the sample.
The device can include probes that guide or propagate light and may include waveguides, optical fibers, or a combination of these. In addition the probes can include an internal reflector. In a various embodiments the reference arm or delay arms are located along with the detector and processor separately (remotely) from the sample or probe arms.
The various sensors and apparatus of the invention can be used to characterize objects, tissues, and material samples. The method includes contacting the material(s) with a sensor having two or more probe or sample arms. Each probe arm of the sensor can have an adjustable delay, the probe arms and reference section or interferometer coupled together and configured such that an interference between backscattered source light from the sample for two or more probe arms and reference light are resolved during a single trace of one or more variable delays of the device. Interference between backscattered source light from each probe arm and reference section light in a single trace of the reference arm is used to characterize the material.
Preferably the low coherence interferometric signals from the two or more sample or probe arm are separated from each other by an amount that permits at least partial sampling of a material or tissue into two or more areas or regions. Preferably there is complete separation of the low coherence interferometric signals from each of the sample or probe arms, however incomplete resolution may also be useful in characterizing a material. In one embodiment, the interference detected for each of the two or more probes provides a characterization of the material. For example the interference may be used to characterize the repair of damaged tissue following surgery, the detection of a disease state of a tissue, or the presence of debris in a compressor or conduit. A preferred version of the invention is to use the apparatus to detect vulnerable plaque in a patient.
Because the devices of the present invention are capable of resolving low coherence interferometric signals that result from backscattered light collected by multiple sample arms in a single trace of an adjustable delay, the invention advantageously eliminates the need for optical switches to resolve LCI signals from multiple sample arms and eliminates the need for the use of multiple interferometers. In applications requiring the collection of several LCI traces in a short period of time, either from a single region or from several regions or directions, the collection of multiple information in a single trace will reduce the time for data collection and interpretation. For example, in probing the circumference of an artery, a single trace will enable rapid identification of a radial position with vulnerable plaque as compared with healthy tissue, and enable selection of probing regions along that radial position only. The identification can be done by comparing the various components of a trace, addition and or subtraction, to quickly determine differences, common features, and provide diagnosis.
Because the sample arms and probe arms, as well as reference arms and delay compensators in versions of the invention can be coupled to existing low coherence light sources, detectors, and processors, the fabrication of removable, interchangeable, or configurable sensor devices is possible.